In the art of conventional hand-held drills, stationary drills, tapping machines, or other kinds of machines used for boring holes in work products, when chips resulting from the boring process accumulate, the load on the driving motor may increase to the extent that an overload on the driving motor results. It would be desirable, however, that when the work load is increased to a predetermined level, that is a predetermined overload level, the drive motor would reverse its direction of rotation so that the cause of the overload, e.g. the chips, could be eliminated, e.g. the chips discharged. Once the chips would be discharged, the drive motor could automatically reverse direction again to restore the normal boring operation.
Aside from boring operations, other operations, such as mixing, crushing, and article washing operations, are subject to the onset of an overload condition on the drive motor due to undesired binding of the articles. Similarly, the overload and binding condition may be relieved by an automatic reversal of the direction of rotation of the drive motor. The reversed rotation serves to undo the binding. Once the binding is undone, the drive motor can reverse direction again to resume normal operations of the drive motor.
More specifically, the prior art discloses U.S. Pat. No. 4,412,162 in which a protective system for preventing damage to a work tool is provided during a tool changing operation in an automatic tool changing apparatus in a numerical control machine tool. The protective system monitors the load current of the driving motor for the automatic tool changing apparatus. When the load current reaches an abnormally high current value during the operating period, excluding the motor starting period, the operation of the automatic tool changing apparatus is reversed and then stopped. It would be desirable, however, if an apparatus were provided which could automatically remove a work overload and then automatically resume normal operations.